Ionizing radiation induces oxidative stress and prolonged cell injury through direct and indirect mechanisms. Radiation interacts with cellular macromolecules, causing oxidative damage that spreads to neighboring cells via redox-modulated communication. Organisms respond with transient molecular, cellular, and tissue-level mechanisms to counteract radiation toxicity. Metabolic pathways are activated during and shortly after exposure, but their effectiveness depends on radiation dose, dose-rate, and quality. When harmful effects exceed homeostatic processes, biological changes persist and may affect progeny cells. Physiological reactive oxygen and nitrogen species (ROS/RNS) are crucial for cellular functions, but their levels may increase in irradiated cells due to oxidative metabolism and chronic inflammation, contributing to long-term genomic instability. Mitochondria play a key role in delayed radiation effects, with defects leading to accelerated aging and various pathologies. Radiation types vary in linear energy transfer (LET), affecting mitochondrial physiology. ROS/RNS from water radiolysis and mitochondrial dysfunction cause DNA damage, mutations, and neoplastic transformation. Radiation-induced oxidative stress can propagate to bystander cells, leading to persistent oxidative damage and genomic instability. Mitochondrial DNA damage and mutations may contribute to heritable traits and genomic instability. Radiation-induced mtDNA deletions and nuclear insertion may alter gene expression and contribute to cancer and aging. Mitochondrial protein import and metabolic enzymes like aconitase are affected by radiation, leading to oxidative stress and cellular dysfunction. Antioxidant defenses, including SOD, glutathione, and catalase, are modulated by radiation, but their effectiveness depends on dose, dose-rate, and LET. Understanding these mechanisms is crucial for mitigating radiation-induced health effects.Ionizing radiation induces oxidative stress and prolonged cell injury through direct and indirect mechanisms. Radiation interacts with cellular macromolecules, causing oxidative damage that spreads to neighboring cells via redox-modulated communication. Organisms respond with transient molecular, cellular, and tissue-level mechanisms to counteract radiation toxicity. Metabolic pathways are activated during and shortly after exposure, but their effectiveness depends on radiation dose, dose-rate, and quality. When harmful effects exceed homeostatic processes, biological changes persist and may affect progeny cells. Physiological reactive oxygen and nitrogen species (ROS/RNS) are crucial for cellular functions, but their levels may increase in irradiated cells due to oxidative metabolism and chronic inflammation, contributing to long-term genomic instability. Mitochondria play a key role in delayed radiation effects, with defects leading to accelerated aging and various pathologies. Radiation types vary in linear energy transfer (LET), affecting mitochondrial physiology. ROS/RNS from water radiolysis and mitochondrial dysfunction cause DNA damage, mutations, and neoplastic transformation. Radiation-induced oxidative stress can propagate to bystander cells, leading to persistent oxidative damage and genomic instability. Mitochondrial DNA damage and mutations may contribute to heritable traits and genomic instability. Radiation-induced mtDNA deletions and nuclear insertion may alter gene expression and contribute to cancer and aging. Mitochondrial protein import and metabolic enzymes like aconitase are affected by radiation, leading to oxidative stress and cellular dysfunction. Antioxidant defenses, including SOD, glutathione, and catalase, are modulated by radiation, but their effectiveness depends on dose, dose-rate, and LET. Understanding these mechanisms is crucial for mitigating radiation-induced health effects.